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Effect of summer rainfall on seed losses of two forage legumes, in the wheatbelt of western Australia

H.M. Saoub, G.B. Taylor, and W.R. Stern

University of Western Australia, Crop and Pasture Sciences, Nedlands WA 6009
CSIRO, Division of Animal Production, Wembley WA 6014

In 1990, we studied the effect of summer rains on seedling establishment and losses, at two sites in the wheatbelt of Western Australia.


Seedling emergence was studied in pastures beginning their second year at Beverley (average annual rainfall 430 mm) and their third year at Merredin (average annual rainfall 320 mm). Two forage legumes were used in this study, Medicago polymorpha cv. Santiago and Trifolium subterraneum cv. Dalkeith. Plant counts were made on 4 paired cores (0.01 m2) taken from each of 4 replicate plots (200 m2). The first counts were made after heavy unseasonal rain on 28- 29 January 1990 and at various intervals thereafter.

Results and discussion

Rainfall relevant to each sampling time is shown in Table 1, together with the associated plant counts. Despite the smaller reserve of Dalkeith seeds in November 1989 there were generally high numbers of Dalkeith seedlings as compared to the Santiago. This behaviour reflects the much higher rate of seed softening in Dalkeith. Substantial numbers of seedlings were lost during the drought conditions experienced during March at Beverley, and during February and April at Merredin. The decline in the seed reserve between November 1989 and June 1990 at Beverley, where there was no over-summer grazing, ranged from 21% for Santiago to 51% for Dalkeith. The corresponding seed losses at Merredin were much higher, ranging from 47% for Santiago to 85% for Dalkeith, and can be attributed to the combined effects of more rapid seed softening in this drier environment together with some seed losses through summer grazing.

Table 1. Changes in seed numbers and plant density (no./m2) in 1989-90.

Successive germ inations of different strains of Trifolium subterraneum following late summer and early autumn rain were also observed in 1963 in the wheatbelt of Western Australia (1), and at ICARDA, Syria (2).


Cocks, P.S. 1988. Pasture, forage, and livestock program. ICARDA, Syria. p.40.

Taylor, G.B. and Rossiter, R.C. 1967. Aust. J. Exp. Agric. Anim. Husb. 7,25-32.

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